This invention relates to a heat-sensitive record material and particularly to a heat-sensitive record material having a color developing layer on which sharp color images can be developed when subjected to a thermal printing treatment. This invention also relates to a method for the production of the heat-sensitive record material of such a kind like that.
There has heretofore been known a heat-sensitive record material which utilizes color reaction between an electron-donating color forming material (hereinafter referred to as "color former") and an electron-accepting acidic reactant material (hereinafter referred to as "acceptor") which the two components being thermally brought into intimate contact with each other to produce a developed color image.
One of the most typical heat transmission systems for developing a color image on the above mentioned heat-sensitive record material is to transfer heat to the heat-sensitive record material through the utilization of a thermal head having a number of electric resistance heating elements in the form of a dot matrix through which Joule heat produced by electric current pulses in response to signals to be recorded can be transmitted to the surface of the heat-sensitive record material when the thermal head is in close contact with the heat-sensitive record material.
In this type of heat transmission a sharp record image can only be obtained by developing a color image exactly corresponding to the heated dots as heating elements of the thermal head.
It is conventional to smooth the color developing layer surface of a heat-sensitive record material by a calendering treatment with use of a supercalender or gloss calender to improve the affinity of the color developing layer surface to a thermal head. In Japanese Patent Publication No. 20,142 of 1977 it was proposed to treat the color developing layer surface of a heat-sensitive record material so as to have a Bekk surface smoothness of 200 to 1000 seconds. U.S. Pat. No. 4,032,609 issued June 28, 1977 discloses a heat-sensitive record material having a Bekk surface smoothness of 100 to 500 seconds. However, a color image exactly corresponding to the heated dots of a thermal head cannot always be obtained by a mere calendering treatment to achieve such a high Bekk surface smoothness as disclosed in those patent specifications since usually each of the dots of a thermal head has such an extremely small size as about 200 microns. In many cases during repetition of heating and cooling the thermal head some molten ingredients of the heat-sensitive composition of the record material are deposited and piled on the thermal head. This "piling" phenomenon results in producing blurred color images having a reduced density. Also "sticking" between the color developing surface and the thermal head occurs. "Sticking" involves a peeling-off noise and results in producing an undesirable deformed color image. In addition, the higher the Bekk surface smoothness, the more glossy the surface of the record material. The record material having an extremely high gloss is of no commercial value because of its unnatural appearance.
The primary object of the invention is to provide an improved heat-sensitive record material in which "piling" and "sticking" can be prevented to the utmost extent with the result that a sharp and clear color image can be developed exactly according to the heated dots of a thermal head.
Another object of the invention is to provide an improved heat-sensitive record material which can satisfactorily meet the requirements of recording machines and implements.
A further object of the invention is to provide an improved heat-sensitive record material which has a natural appearance and is of a high commercial value.
A still further object of the invention is to provide an improved method for the production of the heat-sensitive record material of such the kind.
Other objects and advantages of the invention will be apparent from the following detailed description.